Methods for growing crystals from a liquid melt are known in the art. For example, U.S. Pat. No. 7,097,707, issued to Xu, entitled “GaN boule grown from liquid melt using GaN seed wafers” is directed to methods for making single crystal GaN boules. A first method comprises the procedures of contacting a GaN seed wafer with a GaN source environment under process conditions. The process conditions include a thermal gradient in the GaN source environment for producing growth of gallium nitride on the GaN seed wafer, thus forming the GaN boule. The source environment can be selected from a gallium melt and a nitrogen source or a supercritical ammonia containing solubilized GaN.
A second method comprises the procedures of providing a gallium melt and contacting a GaN seed wafer with the gallium melt in the presence of a nitrogen source and under a thermal gradient. This produces the growth of gallium nitride on the GaN seed wafer, thereby forming a GaN boule. The GaN seed wafer is attached to a rotatable rod. The rotatable rod is rotated, thus rotating the GaN seed wafer, while pulling the rod and the GaN seed wafer from the gallium melt during the growth of the GaN boule. The nitrogen source comprises a nitrogen plasma including atomic nitrogen, nitrogen ions and dinitrogen ions. Also an ambient environment is formed of the gallium melt and the GaN seed wafer. The nitrogen plasma is generated by a discharge technique selected from direct current discharge, radio frequency discharge and microwave discharge. The temperature of the gallium melt is from about 900° C. to about 1500° C. A GaN crust is formed on a surface of the gallium melt, from the reaction between the nitrogen source and the gallium melt. The thermal gradient comprises a temperature which is higher at the GaN crust than at the GaN seed layer, whereby gallium nitride is transported from the crust to the growth of gallium nitride on the GaN seed wafer via dissolved atomic nitrogen in the gallium melt. The GaN in the crust is decomposed into atomic nitrogen with an equilibrium concentration at the temperature at the crust. The atomic nitrogen equilibrium concentration is at supersaturation relative to the temperature at the GaN seed wafer, thus producing homoepitaxial growth of GaN at the seed wafer.
U.S. Pat. No. 7,892,513, issued to Fujiwara, et al., entitled “Group III nitride crystal and method of its growth” is directed to a crystal growth method. The method comprises the steps of preparing a substrate having a principal face and including, at least on its principal face side, a group III nitride seed crystal having the same chemical composition as a group III nitride crystal. The average density of threading dislocations along the principal face is 5×106 cm−2 or less. The method further comprises the step of bringing a solution, in which a nitrogen containing gas is dissolved into a group III metal containing solvent, into contact with the principal face of the substrate, to grow the group III nitride crystal onto the principal face of the substrate.
PCT International Patent Application Publication No. WO 2008/102358 A2, to Einav, assigned to Mosaic Crystals, entitled “Group-III Metal Nitride and Preparation Thereof” is directed to a method for forming a group-III metal nitride material film attached to a substrate. The method includes the procedures of subjecting the substrate to an ambient pressure of no greater than 0.01 pascals (Pa) and heating the substrate to a temperature of approximately between 500° C.-800° C. The method further includes the procedures of introducing a group-III metal vapor to the surface of the substrate at a base pressure of at least 0.01 Pa until a plurality of group-III metal drops form on the surface and introducing active nitrogen to the surface at a working pressure of between 0.05-2.5 Pa until group-III metal nitride molecules form on the group-III metal drops. The method further includes the procedure of maintaining the working pressure and the active nitrogen until the group-III metal nitride molecules diffuse into the group-III metal drops thus forming nitride/metal solution drops. The method finally includes the procedures of maintaining the working pressure and the active nitrogen until the nitride/metal solution drops turn into a wetting layer on the substrate and continuing to increase the concentration of group-III metal nitride molecules in the wetting layer until all the group-III metal atoms contained in the wetting layer are exhausted, and the wetting layer transforms into a group-III metal nitride film.
EPO Patent Application Publication No. EP 1 803 839 A1, to Kasai et al., assigned to Sumitomo Electric Industries, entitled “Fabrication method and fabrication apparatus of group III nitride crystal substance” is directed to a fabrication method of a group III nitride crystal substance. The method includes the steps of cleaning the interior of a reaction chamber by introducing HCl gas into the reaction chamber and then vapor deposition of a group III nitride crystal substance in the cleaned reaction chamber. The HCl gas effectively cleans deposits adhering to the interior of the reaction chamber during crystal growth. The step of cleaning the interior of the reaction chamber can be carried out under the conditions that the HCl gas partial pressure is at least 1.013 hectopascals (hPa) and not more than 1013 hPa, and the temperature in the reaction chamber is at least 650° C. and not more than 1200° C.
The apparatus includes a reaction chamber formed in a reactor tube, a group III element raw material gas generation chamber, an HCl gas introduction pipe to introduce HCl gas into the reaction chamber, an HCl gas introduction pipe to introduce HCl gas to the group III element raw material gas generation chamber, a group III element raw material gas introduction pipe to introduce the group III raw material gas generated at the group III element raw material gas generation chamber into the reaction chamber, a nitrogen raw material gas introduction pipe to introduce nitrogen raw material gas into the reaction chamber, a gas exhaust pipe to discharge gas from the reaction chamber and a substrate holder to dispose an underlying substrate to grow a group III nitride crystal substance in the reaction chamber. The reaction chamber includes a crystal growth zone that is the region in close proximity to a substrate holder. A protection member of the reaction chamber can be disposed on the inner wall of the reaction chamber at this crystal growth zone. Furthermore a device to trap ammonium chloride can be attached at the inlet and/or outlet of the gas exhaust pipe. The configuration is used to grow a group III nitride crystal substance by HVPE.
An article to Gogneau et al., entitled “Surfactant effect of gallium during the growth of GaN on AlN(0001) by plasma-assisted molecular beam epitaxy,” published in Applied Physics Letters, Vol. 85, No. 8, Aug. 23, 2004, is directed to the study of a growth mode of N-face GaN(0001) deposited on an AlN(0001) substrate by plasma-assisted molecular beam epitaxy (PAMBE). With a substrate temperature of 730° C. and a gallium (Ga) flux of ≧0.09 ML/s, Gogneau et al. demonstrated that Ga droplets begin to form on the surface of the AlN(0001) substrate, thus resulting in the formation of a 1 ML dynamically stable Ga film on the surface of the AlN(0001) substrate. The role of the excess Ga during epitaxial growth of GaN was then determined by monitoring the variation of the Bragg spot intensity in the RHEED pattern during the deposition as a function of the GaN deposition time and impinging Ga fluxes. According to the variations in the Bragg spot intensity in the RHEED pattern, Gogneau et al. were able to determine that the Ga in the Ga film behaves as a surfactant during the growth of GaN on AlN(0001) by PAMBE.